Coat proteins of non-enveloped, icosahedral viruses must perform a variety of functions during the virus life cycle, such as assembly of the coat protein subunits into a closed shell, specific encapsidation of the viral nucleic acid, maturation of the capsid, interaction with host receptors and disassembly to deliver the genetic information into the newly-infected cell. A thorough understanding of the multiple capsid properties at the molecular level is required in order to identify potent targets for antiviral therapy and the prevention of viral disease. The systems we have chosen for study are the astroviruses, a family of icosahedral, single-stranded RNA virus that is a causative agent of gastroenteritis in both humans and animals. Very little is known about what regions of the coat protein contribute to the diverse capsid functions. The objective of this application is to test whether novel structural predictions we have made based on the coat protein sequence of the human astroviruses are exhibited in biological experiments. We hypothesize that the assembly and RNA packaging functions of the astrovirus coat protein constitute an individual, modular domain that is distinct from the determinants required for receptor binding and internalization. Our specific aims are: (1) To test whether functional predictions of regions of the coat protein required for virion assembly, particle maturation, and RNA encapsidation are exhibited in biological experiments, by characterizing the phenotypes of a series of mutations. (2) To test the modularity of the coat protein "assembly domain" by constructing chimeric coat protein molecules between different serotypes and species of the Astroviridae. The rationale for these studies is that insight into the molecular mechanisms of astrovirus assembly, nucleic acid packaging, maturation and tropism will inform us of unique and shared properties of astrovirus coat proteins. In addition, the potential to engineer chimeric astrovirus particles that display specific epitopes on the surface of the particle could have practical applications such as generation of particle-based vaccines. Chimeric astrovirus particles displaying surface antigens of related gastroenteritis virus such as norovirus, a Category B bioterrorism agent, could be developed as a polyvalent, preventative vaccine. In the long term, we expect that this work will add not only to the understanding of astrovirus particle biology, but also lead to the development of therapeutic drugs or vaccines to combat viral gastroenteritis in humans. [unreadable] [unreadable]